Utrecht: The river fort of Traiectum

The foundation date of the city of Utrecht is usually equated to the erection of a Roman castellum called Traiectum (Latin for ford or crossing) as part of the Limes Germanicus around the year 50. This square fortress was located on a sideway of the main Roman Road from Lugdunum Batavorum (Katwijk) to Colonia Ulpia Traiana (Xanten) and can still be located around the Dom Square right in the heart of the city of Utrecht. It is located between the Oude Gracht (Old Canal) and Kromme Nieuwe Gracht (Crooked New Canal). The fortress was erected to defend the border of Germania Inferior against invading Frisian and German Tribes from the north. A string of such forts ran along the Rhine river from the coast to the foothills.

In red the castellum Traiectum on the map of the historic city of Utrecht. In Yellow the old routes, these are not the Roman road this ran further south from west to east.

The fortress was destroyed several times by invaders and also the location on a low sand dune by the Rhine meant that floods were a constant assault on its stability. The first fortress was constructed with earth banks later topped with a palisade. Later fortresses were constructed from wood with an embankment around it. The last of the castellae was built in stone and bricks. The fortress also boasted a little harbour: the river itself being the most reliable means of transport in the marshy terrain.

Looking at the current location within Utrecht the castellum doesn't seem to be located on a major river. This position might seem puzzling but one needs to take into account that the landscape looked very different in Roman times. If we superimpose the old flow channels of the Rhine (Rhenus in Latin) the image changes completely. Now the castellum of Traiectum is located in a sharp bend of the river just before it forks and gives way to the Vecht (Fectius in Latin). The fort itself is located on a low land dune and probably had a moat on the land side thus being secure on all sides. In Roman times this branch of the Rhine river with little slope was already silting up as a result of the rise in sea level. Also a dam to lead more water into the Waal river near Nijmegen (Noviomagus) decreased the flow in the Rhine. This in turn lead to a dramatic rise in groundwater levels and the already marshy area become difficult to navigate and go across as the rivers were turning into narrow streams unfit for large vessels. Traiectum was finally abandoned around 270 AD. It seems though that people remained to live here.

The location makes more sense with the old river Rhine projected on the map (in deep blue), showing the fort Traiectum (T) on a low sand dune surrounded by water. These dunes (in amber) forced the water to take several twists and turns and also provided a higher living space for local people in a vicus (v) on either side of the fort. In light blue an even older branch of the Rhine that had mostly silted up by Roman times. This shows how changeable this landscape was.